1. Field of the Invention
The present invention relates to a computer system comprising plural devices, a computer apparatus receiving access from an external device, and a power supply control method for the computer apparatus.
2. Description of the Related Art
To reduce power consumption, a computer apparatus, such as a personal computer (PC), can shift to power saving modes for stopping the power supply to each part of PC and including a sleep mode, a hibernation mode, and a shutdown mode while an idle state without input is continued for a predetermined time.
In addition, if a user operates the power or sleep button provided on the PC, the computer can also shift to a power saving mode. Furthermore, a notebook PC, which is foldable between the main body with the keyboard and the display, can shift to a power saving mode by sensing the closing of the display with a sensor or switch.
In a PC events are generated by the operation of trigger devices such as a sensor and a switch, which senses for example the power button, the sleep-button, and the opening or closing of the display. When these events are detected by BIOS (Basic Input/Output System), the BIOS notifies the OS of the generation of these events. Subsequently, the OS instructs a power controller, which controls power supply to each device connected to the PC, to shift to a power saving mode, and then the power controller performs power-control according to a predetermined power saving mode.
In the recently established ACPI (Advanced Configuration and Power Interface), power saving modes are classified into five levels, i.e., S1 to S5. S1 to S3 are stand-by modes, S4 is a hibernation mode, and S5 is a shutdown mode. In this classification, the power saving modes are established such that power consumption decreases gradually from S1 to S5.
All of the five-level power saving modes comprising S1 to S5 are not required to be implemented in a PC. As an example, only S1 and S3 as a stand-by mode can be or are supported. Such power saving modes are established by PC manufacturers who predetermine the correspondence between events occurring in trigger devices, which shift the PC to a power saving mode, and power saving modes.
As described above, in the conventional technique, the OS, notified by BIOS which detects events from trigger devices, supports shifting to each power saving mode.
As is well known in the art, the OS is a highly general-purpose system for adaptation to various PCs. Therefore, once the OS receives a notice, which relates to shifting to a power saving mode, from the BIOS, the OS solely performs the process of shifting to the power saving mode according to the notice.
Recently, PCs are employed in various situations, being combined with an external device, such as a digitizer, a docking station, and PDA (Personal Digital Assistants). In such usage-situations, the conventional method for shifting to power saving modes, which is controlled only inside the PC, may cause the external device not to access the PC due to the state of a power saving mode. Thus, there remain problems in controlling the shift to power saving modes corresponding to various situations.